Cyclic process for absorption and regeneration of acidic gases

ABSTRACT

The present invention describes the process of preparing ceramics for the absorption of ACIDIC gases, which worsen the greenhouse effect, that are released in combustion systems, or that are present in closed environments. In relation to carbon dioxide, principal target of the present invention, the process of absorption, transport, processing and transformation of the gas into other products is described. The process uses ceramic materials prepared through the solid mixture of one or more metallic oxides, with one or more binding agents and an expanding agent. The product generated can be processed and the absorbent system regenerated. The carbon dioxide obtained in the processing can be used as analytic or commercial carbonic gas, various carbamates and ammonium carbonate.

This application is the U.S. national phase under 35 USC 371 of IntlApplication No. PCT/BR2010/000075, filed on 12 Mar. 2010, whichdesignated the U.S., and claims priority benefit of Application Nos. BRPI0903159-6 filed 13 Mar. 2009 and BR 0000220907705453 filed 5 Mar.2010. The entire contents of each of the foregoing are incorporated byreference herein.

FIELD OF APPLICATION

The present invention describes the process for preparing ceramics forthe absorption of ACIDIC gases, which worsen the greenhouse effect, thatare released by combustion systems or are present in closedenvironments. In relation to carbon dioxide, we describe the main goalof the present invention as a process of absorption, transport,processing, and transformation of the gas into other products. Theprocess uses ceramic materials prepared through the solid mixture of oneor more metallic oxides with one or more binding agents and an expandingagent. The product thus generated can be processed and the absorbentsystem regenerated. The carbon dioxide obtained during the processingcan be used for either analytic or commercial carbonic gas, variouscarbamates, and ammonium carbonate.

STATE OF THE ART

The emission of “greenhouse effect” gases such as methane (CH₄), carbondioxide (CO₂), sulfur dioxide (SO₂), sulfur trioxide (SO₃), the nitrogenoxides, as well as hydrocarbon compounds has caused a series of climaticchanges that are unfavorable for sustaining life. Phenomena can be citedsuch as the prolonging of periods of drought, storms of catastrophicdimensions, hurricanes and tornadoes in regions that never had thosetypes of climatic phenomena, in addition to the global rise in thetemperature of the atmosphere and of the oceans. Associated with theseclimatic changes are also the forming of ACIDIC rain that is intensifiedby the presence of ACIDIC gases and the intrinsic pollution found in theparticulate material and toxic substances that make up that part of theatmosphere which makes direct contact with practically every aerobicorganism present in the biosphere.

The emission of “greenhouse effect” gases are caused mainly byindustrial methods in strategic sectors of the global economy such assteel, concrete, thermoelectric plants, among others. In large urbancenters another worsening factor is present, which is the emission ofpolluting gases provided by methods of transport which use fuels basedon carbon (gasoline, diesel, natural gas, alcohol). As they are fuels offossil origin (gasoline, diesel, coal), they are considerably morepolluting than fuels available from renewable sources (alcohol andbiodiesel).

Future climatic projections signal the immediate necessity for theimplementation of effective procedures to control the emission ofpolluting gases. The use of environmentally friendly technologies basedon solar, hydrogen, wind, and other forms of energy are still out reachfor many industrial processes. The use of renewable and carbon-basedenergy sources, such as ethanol or biodiesel, for example, increaseenergy efficiency and diminish greenhouse gases emission, principally ofcarbon dioxide (CO₂). However, they will continue to emit an intrinsicamount of CO₂ during the burning process, which is an inherent chemicalreaction of combustion. The development of this type of technology,focused on the reduction of greenhouse gases emission, has beensupported by public policies that set limits for the emission of gases.For example, the European Union established a limit of 120 g/km of CO₂for passenger cars until the year 2012, while the current limit is 160g/km. Following this limit will result in a 25% reduction of thepollution caused by small vehicles, which currently contribute withapproximately 15% of global pollution. Other legislation is focused onestablishing maximum limits on emissions from industrial plants, such asthe steel and cement industries, in addition to taxes on processingmethods related to pollution. However, all of these legal restrictionsimposed on production systems that emit greenhouse gases are notsufficient to stop the growing levels of polluting gases that areemitted, as can be verified by reports from the UN(http://www.onu-brasil.org.br, December 2008). It is worth adding thatthe largest contribution to global pollution comes from industry, whichcorresponds to approximately 70%(http://gaoli.sites.uol.com.br/arpolu.htm, December 2008) of globalpollution.

Still related to the development of incentive policies for the reductionof the emission rates of greenhouse gases, one can look to the KYOTOProtocol which suggests that the more developed countries, which areresponsible for more than half the emissions in the world, develop andimplement technologies that reduce the quantity of greenhouse gases intheir own territories or in other countries. The financing of thesetechnologies is paid through carbon credits, which are defined as oneton of CO₂ either not emitted into, or else removed from, the atmosphereas equaling one carbon credit. These are currently (2009) assessed atR$30.00 (http://www.pointcarbon.com/, 27 Oct. 2009). So, businesses thatdevelop environmentally sound methods supported by the KYOTO protocol,or that have among their objectives, the decontamination of theatmosphere, can acquire resources through the sale of carbon credits instock markets.

The objective of various technologies dedicated to reducing the emissionof polluting gases consists of stopping those that are released fromentering into the atmosphere through chemical treatments that catch themin a condensed state (liquid or solid).

As carbon dioxide is the main pollutant and the worst contributor to thegreenhouse effect, there are various technologies described in the stateof the art that propose methods for reducing the quantity emitted. Ingeneral, those methods are focused on two objectives, the first relatingto the permanent containment of CO₂ and the second relating to the reuseof CO₂ for the production of useful products and/or of products ofindustrial interest.

To show the relevance of the process and the complexity of theabsorption of ACIDIC gases produced by combustion systems or present inclosed environments, various patents, methods, and apparatus can befound in the state of the art. Initially, the objective of theinventions had been the absorption of toxic gases in closed environmentssuch as, for example, submarines and breathing devices with the refluxof anaesthetic gases. To purify the air in submarines (absorption ofCO₂) the document GB 190603570 (Winand, P.; “Process for the Eliminationof Carbon Dioxide from the Gaseous Combustion Products of CombustionEngines”, 1906) describes an absorbent mixture of ammonia with sodiumoxide or potassium oxide, as they are produced during the making ofcombustible O₂ (for burning) in the internal combustion engines that aredesigned for the propulsion of submarines. Still related to theatmosphere in submarines, the U.S. Pat. No. 2,545,194 (Colburn, A. P.;Dodge, B.; “Adsorption process for removal of carbon dioxide from theatmosphere of a submarine”, 1951) describes only the use of lithiumoxide for the absorption of CO₂, because a smaller mass is sufficient tomaintain the quality of air for the crew. With the development oftechnologies for the exploration of space, the absorption of CO₂ inclosed environments assumes a position of higher importance, as isdemonstrated by the U.S. Pat. No. 7,326,280 (Hrycak, M. B.; Mckenna, D.B.; “Enhanced carbon dioxide adsorbent”, 2005) applied to thepurification systems of spacecraft (rockets) and space stations with theuse of lithium oxide.

The large-scale application of carbon dioxide absorption processes inclosed environments can be demonstrated by U.S. Pat. No. 5,087,597(Orlando, L. et al.; Carbon dioxide adsorbent and method for producingthe adsorbent, 1992) described as having a mixture based onpoly(alkoxysilane), silicon, aluminum, and iron oxide, which are used inthe absorption of CO₂ present in containers used to transport materialssusceptible to decomposition in ACIDIC environments or for the transportof animals.

Another highly important application corresponds to the absorption ofCO₂ in devices for anaesthetic gases. These devices must have a systemto absorb CO₂ exhaled by the patient; meanwhile, the absorbent materialsmust not react with the anaesthetic substances, such as occurs inabsorbent systems composed of alkaline metals. In this case, thedocument BR 8613138 (Amstrong, J. R.; Murray, J.; “Absorbing carbondioxide used in anesthesiology, and a process of preparing the same”,1997) proposes the substitution of lime by a mixture of calciumhydroxide, plaster, aluminum, and a hygroscopic agent (calciumchloride). Similarly, the document RU 2152251 (Imanenkov, S. I.;Aleksandrova, T. I.; Kulakov, N. I.; Putin, B. V.; “Method of synthesisof carbon dioxide adsorbent”, 2000) describes the use of a mixture ofcalcium hydroxide and potassium carbonate for the absorption of CO₂ inrespiratory devices.

For industrial applications, the absorption processes can be achieved inmore varied ways as, for example, described in the document BR 0306705(Johannes, B. T. et al.; Process for removing carbon dioxide from gasmixtures”, 2004) which shows the use of a mixture of water, sulfolane,and an amine secondarily or tertiarily derived from ethanolamine. Theabsorption process is accomplished by spraying an absorbent solutionagainst a flow of gas containing CO₂, H₂S and/or COS. The process thatis described can be performed preferably at a temperature between 50° C.and 90° C. For the absorption of CO₂ in flowing gases, at an ambienttemperature up to about 100° C., various patents can be found thatdescribe the use of zeolites in specific apparatus such as, for example,U.S. Pat. No. 5,531,808 (Ojo A. F.; Fitch, F. R; Buelow, M.; “Removal ofcarbon dioxide from gas streams”, 1996) that uses zeolite-X, and thedocument EP 0173501 (Keith, P. G.; “Process for removing carbon dioxidefrom gas mixtures”, 1986) that uses zeolite-A. The processes ofabsorption of CO₂ through the zeolites are limited by the range oftemperature, owing to the weak interaction that the zeolites presentwith the absorbed CO₂. For higher temperatures, in which the absorptionof CO₂ occurs, material that does not suffer heat decomposition shouldbe used and, preferably, should be activated by the increase intemperature as, for example, described in the document BR 0003340 forthe preparation of a mixture made of magnesium oxide and a carbonate ofalkaline metal (Mayorga, S. G. et al.; “Carbon Dioxide absorbentscontaining magnesium oxide suitable for use under high temperatures, andthe manufacturing process”, 2000). This mixture absorbs CO₂ in atemperature range between 300° C. and 550° C.

In addition to the absorption methods, there also exists the document US2008086938 (Hazlebeck, D. A.; Dunlop, E. H,; “Photosynthetic carbondioxide sequestration and pollution abatement”; 2008) that describesusing the CO₂ produced in industrial plants by injecting it intobiodigesters that contain algae which, through the process ofphotosynthesis, produce biosynthetic fuel oils of industrial interest.

Some palliative methods to block the release of carbon dioxide into theatmosphere can also be found in, for example, the document AU 2008100189(Ferguson, J. I, S.; “Sequestration of carbon in sinking water” 2008),which suggests a method for making deposits of CO₂ at ocean depthsbetween approximately 3,000 and 4,000 meters.

PROBLEM WITH THE STATE OF THE ART

The state of the art for existing technologies to reduce ACIDIC gases isfocused on the immobilization and transport of those gases to anotherplace, in such a way that the saturated absorbent material may bediscarded.

PROPOSED SOLUTION

The success of the goals and environmental treaties recently proposedwill be reached through the development of efficient environmentaltechnologies that make possible the reuse of CO₂ and other pollutinggases. The present patent request is grounded precisely in this view.Through the use of absorbent ceramics for ACIDIC gases, this patent aimsat making a complete cycle between the absorption and the storage ofACIDIC gases, finally turning them into useful products for varioussectors such as, for example, the agricultural and chemical industries.This absorption cycle returns the mass of emitted pollutants toindustrial applications, with the simultaneous recovery of part of theabsorbent material. When this cycle is not performed, the pollutingmaterial is only immobilized and transported to another place, that is,the pollution is merely transferred to another location. Aside from thecreation of waste deposits of saturated absorbent material, however,there is no serious environmental impact because the material that isformed is inert in the environment. Meanwhile, the methods that areavailable so far are ineffective since they only relocate the pollutantmaterial, for example, the ACIDIC gases. The present invention coversexactly this gap, proposing a complete cycle that permits storage,transport, and regeneration of the absorbed ACIDIC gases for use invarious applications. It is important to emphasize the low cost of themethod proposed, and environmental correctness, as it is inert in theenvironment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention describes a method for reducing the emission ofACIDIC gases and contributors to the greenhouse effect that are releasedby combustion systems and industrial plants such as in the steel,cement, and thermoelectric industries, or systems of gas purification.The absorbent material, after its saturation by ACIDIC gases, is thenprocessed thermally or chemically, generating a flow of purified gaswhich is then used in processes of the synthesis of various usefulproducts such as analytical or commercial compressed gas; usefulproducts for the chemical industry for the synthesis of carbonates andrelated ACIDICs; and useful products for the agricultural industry withthe manufacture of carbonates, nitrates, sulfates and sulfites. Thethermal or chemical processing has the capacity to regenerate theabsorbent material, thus creating a cycle of atmospheric cleansing withthe generation of useful products relevant to the various industrialsectors, at a low cost.

The present invention proposes absorbent mixtures containing oxides ofalkaline earth metals, alkaline metals or transition metals that show akinetic reaction favorable to the absorption of carbon dioxide and otherACIDIC gases such as, but not limited to, SO₂, SO₃, NO and NO₂. Theproposed absorbent mixtures also contain a binding (hardener) agent andan expanding agent. The different compositions represented have theproperty of absorbing ACIDIC gases at different temperatures, which canvary from 25° C. to 700° C., as shown below.

Some forms of absorbent mixtures described in the present patent requesthave the capacity to absorb ACIDIC gases in different environments andunder various thermodynamic conditions. Therefore, they are effective indiverse situations such as when rapid or moderate absorption isnecessary, as well as those in which an extremely slow absorption isnecessary. Therefore, the method proposed in the present invention showscontrol that is as much thermodynamic as kinetic. In this way, theproposed technology can be applied to the decontamination of closedenvironments in ambient temperatures (˜25° C.); purification of flowinggases; the absorption of industrially rejected gases (exhaust systems)at temperatures between 50° C. and 600° C., such as in the production ofcoke, sintering of materials, lamination; the absorption of ACIDIC gasesreleased during the burning of fuels in internal combustion engines, inaddition to the intake airflow of internal combustion engines; andenergy production through thermoelectrics, all aiming at improving theefficiency of the process of burning fuels.

The operating cycle of absorbent materials is illustrated in FIG. 1.This illustration makes it possible to observe the ideal couplingbetween the absorption process of polluting gases of ACIDIC nature withmethods of reusing the absorbent material having the capacity to reduceand even extinguish the emission of ACIDIC gases in combustion systemssuch as furnaces that burn fuel, internal combustion engines, andindustrial plants. The method proposes a cycle of reusing the absorbentmaterial which, after its saturation, is collected, exchanged, andanalyzed in order to determine the composition of the absorbed gases.Next, aside from its composition, the saturated material is brought toan industrial plant outfitted for the recovery of the absorbed gas,transforming it into industrial useful material, totally or partiallyregenerating the absorbent material.

The present invention describes the use of a solid mixture composed ofone or more oxides of alkaline earth metals, one or more hydroxides ofalkaline metals, and oxides of transition metals, enhanced with abinding agent and an expanding agent. The mixture of these componentsmust be done in an aqueous medium so that the final solid acquires itsconsistency, and is expanded uniformly, through the action of thebinding and the expanding agent. After the complete homogenization ofthe components, the mixture is left to settle for a period of 1 to 5hours so that the expanding agent, such as pulverized metallic aluminumor calcium oxalate, can act to generate bubbles uniformly throughout theentire mass. The reaction of the expanding agent occurs slightly beforethat of the binding agent, thus permitting the formation of bubbles thatwill be structurally maintained through the gradual, subsequentactivation of the hardening/binding agent, such as: magnesium oxide,bentonite, kaolin, or Plaster of Paris. After a partial hardening of themixture, it is submitted to a process of moderate heating (100° C.-200°C.) for a period from 3 to 72 hours, although not limited to it, toeliminate the excess water. It is subjected thereafter to intenseheating (between 500° C. and 800° C., although not limited to it) for aperiod of 1 hour, although not limited to it, that guarantees thehardening of the mixture. This heating must be done in the presence ofnitrogen or in the absence of airflow; or, in a closed chamber or in theabsence of ACIDIC gases that could be absorbed during the synthesis ofthe material.

In the stage following the homogenization, the material can be shapedinto specific forms, for example, compact blocks, cast blocks (bricks),or pellets of varying sizes (5 a 20 mm), among others. For the shapingof blocks (compact or cast) the mixture can have a more fluidconsistency by the addition of excess water, facilitating itshomogenization. In this case, you can also use a larger amount ofexpanding agent in order to increase the area and the efficiency of theabsorption process. For the shaping of the pellets, the initial mixturemust have a more pasty consistency that makes the manufacture of thepellets possible, which next should be submitted to heating to stop therecombining of the material.

The intense heating stage can be done in an autoclave at a lowertemperature, approximately 200° C. The process guarantees greaterrigidity of the formed solid, giving it greater mechanical resistance.

The absorbent material described in this patent request shows a basic(Translater's Note: opposite of ACIDIC) character, allowing its use inprocesses of the absorption of ACIDIC gases such as carbon dioxide(CO₂), sulfur dioxide (SO₂), sulfur trioxide (SO₃), among others.Although all the gases mentioned worsen the greenhouse effect and ACIDICrains, it is carbon dioxide that appears to be the main pollutant, owingmostly to the increased quantity produced in industries that usecombustion processes. Thus, CO₂ will be used in examples showing thereactions and illustrating the efficiency of the process of absorptionto reduce the emissions of gases which worsen the greenhouse effect. Itwill show the subsequent use of the material formed from theregeneration of the absorbent ceramic, and the creation of importantproducts of high aggregate value, for various industrial sectors.

The potential for the absorption of materials is determined by thekinetic reaction of the gas with the existing oxides. Hence, everymixture has a range of ideal temperatures for absorption, and the speedof absorption depends on the composition, the temperature, and the flowof gas over the material. The ranges of absorbent temperatures and theconditions of regeneration of materials are discussed below,individually, for each type of composition. As previously described, themain focus of this current invention is the absorption of carbondioxide, among others; therefore, the equations below show the chemicalreactions that occur during the process of absorption of the CO2, asidefrom the absorbent mixture containing calcium oxide and potassiumhydroxide, among others.CO_(2(g))+CaO_((s))→CaCO_(3(s))CO_(2(g))+2KOH_((s))→K₂CO_(3(s))+H₂O_((g))

The absorbent material makes the transport and the concentration of theabsorbed gases for industrial installations which are suitable for itsprocessing. The recovery of carbon dioxide can be done through thethermal decomposition of the material, or from chemical treatment withnitric ACIDIC, among others, and subsequent regeneration of absorbentmaterial through the addition of sodium hydroxide, among others, in thepresence of 1-2% of aluminum, among others. The mixture that is formedis filtered and heated to 100° C. in order to eliminate water, thusregenerating the absorbent material.

The carbon dioxide that is formed from the saturated absorbent ceramicshows an elevated concentration, making possible various industrialmethods. Initially, that same carbon dioxide can be compressed andbottled for its subsequent commercialization as an analytic reagent, orin distinct processes that use CO₂ gas. In addition to this directapplication of the CO₂ that was absorbed from polluting industrialplants, two more methods, among others, are proposed in this patentrequest for the chemical transformation of carbon dioxide into variouscarbonates and carbamates, among others.

The carbon dioxide gas can be injected into a basic solution of sodiumhydroxide or ammonium hydroxide, among others. The chemical reactionsfor those processes are shown in equations 1 and 2 (Eq. 1 and Eq. 2).After the formation of the carbonate, the solution of sodium carbonateis heated until the water is completely evaporated (approximately 100°C.), and the ammonium carbonate (when the basic solution that is used isammonium hydroxide) is left to evaporate at 40° C. to avoid thesublimation of the desired material, leaving only the carbonatecorresponding to the base utilized.

The synthesis of ammonium carbamate can be done at room temperature bypassing a stream of CO₂ through a container with liquid ammonia. Thereaction is kinetically favorable, as the immediate formation of a whitesolid is observable. Following this, the system is kept still and thecarbamate can be separated through filtering or decantation, amongothers. The corresponding reaction for this process is shown in thefollowing chemical equation (Eq. 3).CO_(2(g))+2NH_(3(l))→NH₄[H₂NCO₂]_((s)))  Eq. 3

In case the CO₂ is collected in a container with a basic aqueoussolution or a suspension of secondary amines, HNR2, the carbamate ofalkaline metals or of corresponding ammonia can finally be obtained,according to the following equation (Eq. 4).

EXAMPLE 1 Preparation of Class 1 Absorbent Material: Test of the Speedof Absorption and Saturation Time to 90%

The Class 1 absorbent ceramics use MgO as the binding agent, with aconcentration of up to 10% (p/p) and aluminum powder as the expandingagent, with a concentration up to 1%. The rest of the mixture, whichcorresponds to the absorbent components, is composed of mixtures of CaOand La₂O₃ (FIG. 3), CaO and KOH (FIG. 4), CaO and MgO (FIG. 5), MgO andKOH (FIG. 6) with the proportions in defined amounts for every range oftemperature in which the absorption process is more intense than thethermal decomposition process of the saturated material. The mixturescontaining magnesium absorb more effectively between 50 and 400° C.while the mixtures CaO+La₂O₃ and CaO+KOH can be used in the absorptionprocess between 100 and 700° C. The use of MgO as binding agent givesthe material superior mechanical resistance in relation to the bindersbentonite and kaolin as, for example, a sphere of approximately 5 mmdiameter, containing CaO 75% and MgO 25%, resists up to 55N.

For the Class 1 compositions, the potential for absorption is maximizedbecause the binding material (MgO) also has the capacity to absorb CO₂.

Based on the kinetic study of the Class 1 materials it was possible toestimate the storage time (t₉₀) of the absorbent materials, i.e., thetime for the consumption of 10% of the stored material in ambientconditions for the composites with CaO content greater than or equal to80%, to be approximately 15 days. This makes possible the storage andtransportation of the ceramic material for industrial installation whereit will be used for the absorption of CO₂.

EXAMPLE 2 Preparation of Class 2 Absorbent Material: Bentonite

The Class 2 absorbent ceramics use bentonite as the binding agent withconcentration of up to 10% (p/p), and aluminum powder as the expandingagent with concentration of up to 1%. The rest of the mixture, whichcorresponds to the absorbent components, is composed of binary mixturesof CaO and La₂O₃ (FIG. 7), CaO and KOH (FIG. 8), CaO the MgO (FIG. 9).

Bentonite is made of 66.9% SiO₂, 16.3% Al₂O₃ and 6% H₂O; with the mostcommon impurities being Fe₂O₃ (˜3.3%), NaOH (2.6%), Ca(OH)₂ (1.8%) andMg(OH)₂ (1.5%). As mentioned previously, the mechanical resistance ofthe material using bentonite (Table 1) is poorer compared to MgO as abinding agent, but that does not prevent its use as a structuring agentfor absorbent mixtures of CO₂. In the same way, the compositionscontaining CaO+KOH or CaO+La₂O₃ absorb in a range of higher temperature(100 to 700° C.), while the mixture CaO+MgO can absorb between 50 and400° C.

TABLE 1 Content of bentonite and mechanical resistance for mixturescontaining 80% or more of CaO Content of Diameter of bentoniteResistance the sphere (% p/p) (N) (mm) 10 31 5.8 8 44 6.0 6 41 7.4 4 356.9 2 28 6.5

EXAMPLE 3 Preparation of Class 3 Absorbent Material: Kaolin

Class 3 ceramic absorbents use kaolin as the binding agent with aconcentration of up to 10% (p/p) and aluminum powder as expanding agentwith a concentration of up to 1%. The rest of the mixture, whichcorresponds to absorbent components, is composed of binary mixtures ofCaO and La₂O₃ (FIG. 10), CaO and KOH (FIG. 11), CaO and MgO (FIG. 12).This class of materials shows physical and kinetic properties similar toClass 2. Kaolin corresponds to a mixture of aluminosilicates with theempirical formula Al₂O₃.mSiO₂.nH₂O, in which m can assume values from 1to 3 and n can vary between 2 and 4.

To exemplify the efficiency and the speed of the absorption of the Class2 materials, a composition containing 88.5% CaO, 1% KOH, 10% kaolin and1% aluminum was used. The absorption experiment was performed with aflow of CO₂ proportional to the mass of the absorbent, including 26grams of CO₂ per minute per gram of ceramic material (26 g·min⁻¹g⁻¹).The average speeds of CO₂ absorption, at different temperatures for theanalyzed mixtures, are found in Table 4, along with the time forsaturation of 90% of the material. In composites containing higher KOHcontent, the speed of absorption increases considerably, up to 10%faster, however, due to the stoichiometric proportions of the material,efficiency is impaired.

TABLE 2 Speed of absorption and time to saturation for 90% of theceramic material composed of 88.5% CaO, 0.5% KOH, 10% kaolin and 1%aluminum with exposure to a flow of CO₂ from 26 g · min⁻¹kg⁻¹ per gramof absorbent material. Temperature Speed Time ~90% (° C.) (g ·min⁻¹kg⁻¹) (min) 200 1.2 576 300 12.2 57 400 38.6 18 500 49.7 14 600189.0 4

EXAMPLE 4 Preparation of Class 4 Absorbent Material: Plaster

Class 4 absorbent ceramics use Plaster of Paris as binding agent with aconcentration of up to 10% (p/p) and aluminum powder as expanding agentwith a concentration of up to 1%. The rest of the mixture, whichcorresponds to the absorbent components, is composed of binary mixturesof CaO and La₂O₃ (FIG. 13), CaO and KOH (FIG. 14), CaO and MgO (FIG.15).

Mixtures with a quantity of less than 5% of plaster lose their rigidity,damaging the handling of the material. An inverse relation between thealuminum content and rigidity can be observed, because the excessiveincrease in the quantity of bubbles in the structure of the materialdemands a greater amount of binding agent (plaster). For the process ofabsorbing the carbon dioxide, the temperature of decomposition ofcalcium carbonate in the mixture must be higher than 750° C. The processof regenerating the material demands the addition of an expanding agent(aluminum), reducing thus the concentration of the binding agent andabsorbent in approximately 1 to 2% for every cycle. Therefore,considering the minimum concentration of calcium oxide and Plaster ofParis, every mixture makes it possible to perform approximately 5 cyclesof absorption/regeneration with no considerable loss of efficiency andmechanical resistance of the material. Calcium oxalate can be used asthe expanding agent although it is necessary to treat it thermally sothat, through the decomposition of oxalate to calcium oxide, the carbondioxide generated causes the aeration of the material. In this process,the carbon dioxide needs to be transformed into useful products in theinitial process of the preparation of the ceramic.

EXAMPLE 5 CO₂ Absorption Test

To verify the absorption process, a chainsaw two-stroke engine, whichuses a composite fuel containing 96% gasoline and 4% oil, was used. AClass 2 ceramic, composed of 88% CaO, 1% KOH, 10% kaolin and 2% aluminumwas placed in a tubular furnace at 500° C., in a hood with an exhaustsystem. Then, the motor was started and the discharged gases weredirected to the entrance of the furnace to allow contact of those gasesand the ceramic at the temperature of the furnace. After about 1 hour,the furnace and the engine were shut off. The material obtained wasweighed comparing the difference in mass in relation to the originalmass of the ceramic. A gain in mass showing a 40% absorption wasverified. An elemental analysis of carbon and nitrogen showed anadditional mass related to these elements of about 45% carbon comingfrom the CO₂, and less than 1% nitrogen coming from the nitrogen oxides.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 describes the absorption cycle, the production of useful productsand the recovery of absorbent materials. FIG. 1 outlines the cyclicalprocess proposed in the patent request for the absorption of ACIDICgases and the reuse of them for the synthesis of useful products,regenerating the absorbent material. The process begins with thepreparation of the absorbent material (101), which is made of two ormore oxides of alkaline earth metals or earth alkaline with alkalineoxide, binding agents and expanding agents. The absorbent ceramic isthen exposed to a flow of gas, at a temperature between 50 and 600° C.(110), the saturated material is exchanged (112) and analyzed (113) inorder to determine the type of process that was used in its processing(120), yielding for each composition one or more types of usefulproducts (121). During the processing of the saturated material, theabsorbent ceramic can be regenerated (130) by recomposition and shapedagain (140) being, therefore, ready to be reused in the absorption ofACIDIC gases.

FIG. 2 describes processes of regenerating absorbed carbon dioxide andthe regeneration of absorbent material. FIG. 2 highlights the process ofrecovering the ceramic materials described in the present patent requestafter saturation with carbon dioxide, which does not limit the use ofthe absorbent materials, which can be used for any gas of an ACIDICnature. Initially, the absorbent ceramic (200) is exposed to a flow ofCO₂ at a temperature between 100 and 600° C. The saturated material(210) can be processed in two distinct ways. The first way correspondsto the thermal decomposition of the carbonates produced at a temperatureof approximately 800° C. (260). In this way, the released CO₂ (250) isbrought to the processing systems of industrial interest. The carbondioxide can be stored (251) or transformed into other products such ascarbonate (252) and carbamate (253). The flow of CO₂, which has anelevated percentage of concentration, can be used in the production ofammonium carbamate or various other carbonates such as ammoniumcarbonate or sodium carbonate. The carbon dioxide (250) can also beregenerated through the reaction of the saturated material (210) with anACIDIC (220) such as nitric ACIDIC, among others. The remaining mixtureproduced is alkalinized by the addition of NaOH (230), turning thealkaline earth metal hydroxides and other insoluble hydroxides intoprecipitates, enabling the separation by filtering or decantation. Then,pulverized aluminum is added to complete the process of expanding themass. Finally, the material is heated to remove excess water (240) andfor the hardening of the ceramic material, which is available to restartthe cycle of absorption and the use of carbon dioxide.

FIG. 3 corresponds to the composition of the mixture that is best suitedto each temperature, and which uses MgO as binding agent forming CaO andLa₂O₃.

FIG. 4 corresponds to the composition of the mixture that is best suitedto each temperature, and which uses MgO as binding agent forming CaO andKOH.

FIG. 5 corresponds to the composition of the mixture that is best suitedto each temperature, and which uses MgO as binding agent forming CaO andMgO.

FIG. 6 corresponds to the composition of the mixture that is best suitedto each temperature, and which uses MgO as binding agent forming MgO andKOH.

FIG. 7 corresponds to the composition of the mixture of the absorbentscomprising CaO and La₂O₃, and which are enriched through the addition ofbentonite in temperature ranges at which they can absorb CO₂.

FIG. 8 corresponds to the composition of the mixture of the absorbentscomprising CaO and MgO, and which are enriched through the addition ofbentonite in temperature ranges at which they can absorb CO₂.

FIG. 9 corresponds to the composition of the mixture of the absorbentscomprising CaO and KOH, and which are enriched through the addition ofbentonite in temperature ranges at which they can absorb CO₂.

FIG. 10 shows the composition of material containing kaolin, used forenrichment, comprising CaO and La₂O₃.

FIG. 11 shows the composition of material containing kaolin, used forenrichment, comprising CaO and KOH.

FIG. 12 shows the composition of material containing kaolin, used forenrichment, comprising CaO and MgO.

FIG. 13 correlates the composition of the absorbent material withmixtures containing up to 10% Plaster of Paris comprising CaO and La₂O₃,for all ranges of temperature at which it is possible to use thesematerials.

FIG. 14 correlates the composition of the absorbent material withmixtures containing up to 10% Plaster of Paris comprising CaO and KOH,for all ranges of temperature at which it is possible to use thesematerials.

FIG. 15 correlates the composition of the absorbent material withmixtures containing up to 10% Plaster of Paris comprising CaO and MgO,for all ranges of temperature at which it is possible to use thesematerials.

The invention claimed is:
 1. A cyclic process for preparation and use ofceramic material for absorption of acidic gases, comprising: preparationof absorbent material, absorption of acidic gases, saturation ofabsorbent material, exchange of absorbent material, analysis of thesaturated material, processing of materials, obtaining of productionsinput, regeneration of recovered material, and recomposition of theabsorbent material.
 2. The cyclic process according to claim 1, whereinthe preparation of the material comprises the following steps: a)mixture of components: absorbent agents, binding agent and expandingagent, in an aqueous medium; b) rest of the mixture for a period of 1 to5 hours; c) activation of the expanding agent through homogenization ofthe mixture; d) moderate heating of the mixture to a temperature between100 and 200° C., for a period between 3 and 72 hours; and e) intenseheating of the mixture in the presence of nitrogen or in the absence ofairflow, immediately afterward moderated heating at a temperaturebetween 500 and 800° C., for a period of approximately 1 hour or in anautoclave at a lower temperature of approximately 200° C.
 3. The cyclicprocess according to claim 2, comprising the capability of the materialto be molded into specific forms afterwards the homogenization, step“c”, such as compact blocks, cast blocks (bricks) or pellets of varyingsizes.